1. Technical Field
The present invention relates to a haptic interface and more particularly, but not exclusively, to a method of adjusting such a device to suit individual users.
2. Related Art
After sight and sound, the sense of touch is becoming the third element of multimedia output. The sense of touch is particularly useful to persons with visual impairment and also in training some mentally handicapped people. In order to provide touch stimulation, particularly where electrical signals are used to cause a remote interface to operate, it is preferable and usually beneficial to ensure that the output is perceived by each user in the same way and/or as at the same level.
In the Journal of Experimental Psychology, 64, pp 489-494, S. S. Stevens and J. R. Harris, “The Scaling of Subjective Roughness and Smoothness”, there is discussed the manner in which people perceive roughness or smoothness in a subjective comparative manner. Stevens determined that the perception of roughness is proportional to grit size of sandpaper raised to some power. Later studies by S. J. Lederman, for example (Perception and Psychophysics 16(2) pp 385-395 “Tactile Roughness of Grooved Surfaces; The touching process and effects of macro- and micro-surface Structure”), confirmed that such perception also applied to grooves and bumps.
Now, while each person has a constant perception of comparative roughness or smoothness, there is a variation in which different persons perceive such roughness. So that although “Steven's Law” applies across substantially the whole populace, the variation in perception between persons alters the power to which grit size needs to be raised. This so-called Steven's exponent, once determined for an individual in respect to a surface type, is constant whether the surface texture is grit, groove or bump. Thus it is known that Steven's exponent is constant for different grits, for different grooves and different bumps separately but the exponent will often vary between these, although it is possible to convert the exponent as needed.
Now, in seeking to improve communication between people, particularly for example to provide additional stimulation, in addition to visual or aural stimulation, the provision of haptic information in signalling transmitted across the #STN for example or as an output from a control means requires some form of calibration between users or with an end user.